[blob] Add DB method to query holders by prefix

Summary:
Part of ENG-9367.
Added DB function that queries the holder-tag index and returns found blobHash-holder pairs.

Depends on D13617

Test Plan: Tested together with the next diff

Reviewers: kamil, varun, will

Reviewed By: kamil

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D13618